From DE 36 01 862 C2 a prior-art circuit arrangement is known in which an electric motor connected to an A.C. supply is controlled by means of a Triac. In this arrangement, control is effected such that a Diac with a resistance network is connected to the gate terminal of the Triac, with the value of this resistance network being user-adjustable. By altering the resistance value, the power input of the electric motor is controlled in such a fashion that in the presence of a smaller resistance the electric motor accepts a higher power than in the presence of a greater resistance. In order to limit the starting current when the electrical load is switched on, it is provided that the electric motor has only a low power input when switched on. To accomplish this, it is provided that in the startup phase of the electric motor the full resistance value is connected in the series arrangement with the Diac. Only when startup of electric motor is completed, the motor then fulfilling a specified minimum function, will this full resistance value be bypassed such that the resistance value set by the user is connected to the Diac. The result thereby achieved is that the electric motor can start up with a low power input only, that is, at a low starting current. In the prior-art specification referred to, the fulfillment of the minimum function of the electric motor is derived from the fact that the electric motor involved is the motor of a vacuum cleaner and that a pressure sensor is provided which senses the differential pressure of the delivery side to the suction side of the electric motor, enabling the full resistance to be by-passed by the resistance value set by the user in dependence upon the sensor signal.
It is an object of the present invention to limit currents to be switched to an electrical load reliably with a minimum possible complexity of components.